Metal (lead, zinc, copper, cadmium, iron) uptake, tolerance and radial oxygen loss in typical wetland plants

The present study aims to investigate characteristics of metal tolerance, uptake, root oxygen release and metal tolerance mechanism in wetland plants, and also the effects of root oxygenation on metal speciation and mobility in rhizosphere.; In the field, the results showed that metal accumulation by wetland plants differed among species, populations and tissues. Metals accumulated by wetland plants were mostly distributed in root tissues, suggesting that an exclusion strategy for metal tolerance commonly exists in these plants. The factors affecting metal accumulation by wetland plants include metal concentrations, pH, and nutrient status in substrates. In general, concentrations of Pb and Cu in both aboveground and underground tissues of the plants were positively correlated (P < 0.05) to their total and/or DTPA-extractable, fractions in substrates while negatively to soil N and P, respectively.; The present study indicated that although exposed to a similar level of metals (Pb and Zn) in rhizosphere soil solution, metal uptake by shoots of C. flabelliformis and P. paludosum was greatly reduced, consequently leading to a better performance under flooded than under drained conditions. This may be related to the enhanced Fe plaque in the former, but due to the decreased root permeability in the latter under anoxic conditions. The Fe plaque on root surface has potential to sequester metals and then reduce metal concentration and translocation in shoot tissues. However, whether the Fe plaque acts as a barrier to metal uptake and translocation may be dependent on the root anatomy. The failure of some species such as P. fugax to reduce shoot metal concentrations in flooded substrates and with Fe plaque in hydroponics was possibly due to the high permeability of root cell wall and low ability of cortex to immobilize metals in the fine adventitious roots.; Although metal tolerance in wetland plants mainly depends upon their metal exclusion ability, the higher-than-toxic-level of metal concentrations in some species indicates that internal metal detoxification might also exist. It was suggested that malic or citric acid in shoots of P. paludosum and C. flabelliformis may account for their internal detoxification for Zn. (Abstract shortened by UMI.)...